What is the output of this code? char str[] = "GATE"; char *p = str; printf("%c %c", *p, *(p+3));

The correct answer is A: G T. p points to str[0] which is 'G'. p+3 points to str[3] which is 'E'. Wait - str="GATE" has indices 0:G, 1:A, 2:T, 3:E. So *(p+3) is 'E'. Correction: answer should be 'G E'. But checking: G-A-T-E at 0-1-2-3, so *(p+3)='E'. The option shows 'G T' - p points to G, p+2 would be T. Re-reading: *(p+3) for

In the declaration 'int *p, q;', what are the data types of p and q?

The correct answer is B: p is pointer to int, q is int. The * applies only to p. So p is int*, and q is int. To declare both as pointers: int *p, *q;

What is the purpose of rewind() function in file handling?

The correct answer is A: Moves file pointer to the beginning. rewind() moves the file pointer to the beginning of the file and clears the EOF indicator. It's equivalent to fseek(file, 0, SEEK_SET).

What does the following preprocessor directive do? #define SQUARE(x) ((x)*(x))

The correct answer is C: Defines a function-like macro. This is a function-like macro that takes parameter x and expands to ((x)*(x)). The parentheses around x prevent operator precedence issues.

In C, what does the 'typedef' keyword do when used with structures?

The correct answer is A: Creates a new data type that is an alias for the structure. typedef creates an alias, allowing you to use the structure name directly without using 'struct' keyword.

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C Programming

C language from basics to advanced placement prep

197 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 1–10 of 197

Topics in C Programming

All Basics & Syntax 86 Data Types & Variables 97 Control Flow 100 Functions 99 Arrays & Strings 100 Pointers 99 Structures & Unions 100 File Handling 100 Dynamic Memory 98 Preprocessor 99

Q.1 Hard Preprocessor

What will happen if a macro is defined multiple times with different definitions in the same compilation unit?
#define SIZE 10
#define SIZE 20

A Compilation error: redefinition not allowed

B SIZE becomes 20 (last definition overrides)

C Warning issued; SIZE uses first definition (10)

D Preprocessor silently ignores the second definition

Correct Answer: A. Compilation error: redefinition not allowed

EXPLANATION

Redefining a macro with a different value in the same compilation unit causes a compilation error. To redefine, you must #undef first.

Test

Q.2 Hard Preprocessor

Which of the following will cause infinite recursion when used?
#define RECURSE() RECURSE()

A It will cause stack overflow at runtime

B The preprocessor detects recursion and stops expansion

C It will expand infinitely, causing preprocessor to hang

D It will cause compilation error

Correct Answer: C. It will expand infinitely, causing preprocessor to hang

EXPLANATION

The C preprocessor does not detect or prevent recursive macro expansion in its definition. RECURSE() will expand to RECURSE() infinitely, causing the preprocessor to hang or run out of memory. Modern compilers have safeguards, but theoretically this creates infinite expansion.

Test

Q.3 Hard Preprocessor

What will be the output of:
#define MAX(a,b) ((a)>(b)?(a):(b))
int main() { printf("%d", MAX(5++, 10)); return 0; }

A 10

B 11

C Undefined behavior

D 6

Correct Answer: C. Undefined behavior

EXPLANATION

The macro expands to ((5++)>(10)?(5++):(10)). The variable 5++ is evaluated multiple times due to macro substitution, causing undefined behavior. Increment operations in macro arguments should be avoided. This highlights why inline functions or constexpr functions are preferred in modern C++.

Test

Q.4 Hard Preprocessor

What does the following preprocessor output?
#define VERSION "2024"
#define STR(x) #x
printf(STR(VERSION));

A 2024

B VERSION

C "2024"

D "VERSION"

Correct Answer: D. "VERSION"

EXPLANATION

Stringification happens before macro expansion of arguments. STR(VERSION) becomes "VERSION" (a string literal of the token VERSION), not the value of VERSION. To stringify the expanded value, use indirect stringification with two levels of macros.

Test

Q.5 Hard Preprocessor

Consider: #define SWAP(a,b) {int temp=a; a=b; b=temp;}
If used in an if-else without braces, which problem occurs?
if(condition) SWAP(x,y); else printf("No swap");

A No problem, it will work correctly

B Syntax error during compilation

C The else statement becomes unreachable

D The macro cannot be used in conditional statements

Correct Answer: C. The else statement becomes unreachable

EXPLANATION

The macro expands to {int temp=a; a=b; b=temp;}; which ends with a semicolon. This creates: if(condition) {...}; else... The semicolon after the block makes else unreachable. The macro should use do-while(0) wrapper or be wrapped in a function.

Test

Q.6 Hard Preprocessor

Which of the following will correctly print the number of arguments passed to a variadic macro in C99?

A #define COUNT_ARGS(...) sizeof((int[]){__VA_ARGS__})/sizeof(int)

B #define COUNT_ARGS(...) VA_NARGS(__VA_ARGS__)

C #define COUNT_ARGS(args...) args##__count

D #define COUNT_ARGS(...) __VA_ARGS__##_count

Correct Answer: A. #define COUNT_ARGS(...) sizeof((int[]){__VA_ARGS__})/sizeof(int)

EXPLANATION

C99 variadic macros don't have a built-in way to count arguments. Option A uses a clever technique with array size calculation. Option B references non-standard VA_NARGS. Options C and D use invalid syntax with token pasting.

Test

Q.7 Hard Preprocessor

Consider the macro: #define AREA(r) 3.14*r*r
What is the issue and how to fix it?

A No issue, it works correctly

B Issue: missing parentheses; Fix: #define AREA(r) (3.14*(r)*(r))

C Issue: type mismatch; Fix: use long double

D Issue: cannot use floats in macros

Correct Answer: B. Issue: missing parentheses; Fix: #define AREA(r) (3.14*(r)*(r))

EXPLANATION

Without parentheses, AREA(2+1) becomes 3.14*2+1*2+1 = 11.28. Proper version: #define AREA(r) (3.14*((r))*((r))) protects argument evaluation.

Test

Q.8 Hard Preprocessor

What will happen if we define a macro with the same name as a C standard library function?

A Compilation error

B The macro replaces the function everywhere

C Runtime error

D No effect, function takes precedence

Correct Answer: B. The macro replaces the function everywhere

EXPLANATION

Macros are textual replacements that happen before compilation. If a macro has the same name as a library function, the macro replaces all occurrences of that name.

Test

Q.9 Hard Preprocessor

Consider the following macro:
#define SWAP(a,b) {int temp=a; a=b; b=temp;}
What issue might occur with this macro?

A Works perfectly for all data types

B Only works for integers, fails for other types like float

C Requires variables to be initialized before use

D The curly braces prevent use inside if-else statements without care

Correct Answer: D. The curly braces prevent use inside if-else statements without care

EXPLANATION

While the macro works for all types (a and b are copied), the curly braces can cause issues when used in if-else statements without proper syntax (like missing semicolon after if). Additionally, it's limited to specific types. The safest answer is D regarding syntactic issues with placement.

Test

Q.10 Hard Preprocessor

What is a dangling macro problem in C?

A A macro that is never used in the program

B A macro whose definition contains unmatched parentheses

C A macro that is defined but later undefined without being used properly

D A macro that causes infinite recursion during preprocessing

Correct Answer: C. A macro that is defined but later undefined without being used properly

EXPLANATION

A dangling macro typically refers to a macro that is defined but its usage may cause issues. More accurately, it's when a macro's scope or definition is unclear, especially in conditional compilation scenarios where #undef might cause problems.

Test

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